isolate launcher download from release fetch

app/src/main/res/values/strings.xml

@@ -70,6 +70,7 @@
     <string name="launcher_self_update_failed_title">Update failed</string>
 
     <string name="launcher_self_update_failed">Failed to install launcher update: %1$s.</string>
+    <string name="launcher_update_download_failed">Downloading update failed: %1$s</string>
     <string name="launcher_self_update_progress">Installing update…</string>
 
     <string name="launcher_starting_game">Starting Geometry Dash…</string>